EP3517601A1 - Method and assembly for producing microalgae - Google Patents

Abstract

The invention relates to a method and a plant for the production of microalgae in a tubular thin-film photobioreactor with active temperature control and recycling of a microalgae cultivating solution in phototrophic and mixotrophic Cultivationsweise, being used as a thin-film photobioreactor arranged in parallel glass tubes in which a flexible tube is laid, the free floats in the microalgae cultivation solution and through which a temperature control medium is pumped, which is periodically replaced by air and the culture solution is passed through a circulation container in which a spiral tempering is arranged.

Description

The invention relates to a process and a plant for the production of microalgae in a tubular thin-film photobioreactor with active temperature control and circulation of a microalgae cultivation solution in phototrophic and mixotropher cultivation manner, according to the preambles of claims 1 and 12.

Microalgae are valuable food and feedstuffs that will make a major contribution to the future supply of the growing world population. Microalgae grow in the water. Their production requires much less space than the production of comparable agricultural products.

For industrial production of microalgae several methods are already known and applied.

Thus, methods for the production of microalgae in natural and artificial ponds and basins are known ( H. Matsumoto et al., Applied Biochemistry and Biotechnology, Vol. 51/52, 681, 1995 ). These have the advantage of low investment costs and low operating costs, but the disadvantages of unavoidable contamination of living things, Staubeinwehungen, salination by evaporation losses, low productivity of about 10 g of biomass per m ² d and low product quality.

However, an improvement in product quality can be achieved if the open basins are operated in a greenhouse ( DE 10 2014 011 317 A1 ). But then the investment costs increase, the risk of contamination is lower, but the other disadvantages persist.

Processes for the preparation of microalgae in closed systems have been known for several decades (ia DE 198 14 253 C2 ). They have the principal advantage of avoiding contamination, process optimization and control, higher productivity and better product quality. Disadvantages are higher investment costs and higher operating costs.

A proven method is the cultivation of microalgae in the closed system of tubular thin-film vessels as photobioreactors according to EP 1 040 182 B1 , It allows the production of various microalgae species in high purity with good and stable productivity of daily 0.2 to 0.7 g microalgae biomass per liter of culture solution. This method is suitable for locations in temperate climates. It is not well suited to zones with high temperature spikes during the year and throughout the day as microalgae have optimal growth and living temperatures, depending on the species. Some of the nutritionally important species also die in a culture solution at temperatures above 38 ° C. The arrangement of the photobioreactors in a greenhouse is a condition for practical implementation.

An advance on this is in the application DE 10 2009 045 851 A1 The main advantage is the use of transparent or translucent tubing as tubular thin-film vessels for photobioreactors, preferably of flexible silicone rubber double-chamber tubing, for the cultivation of phototrophic macro- and microorganisms. These hoses can be arranged with little technical effort to a photobioreactor module that they can be adjusted according to the geographical location of the site, the given climatic conditions such as sun gear and temperature. By using the double-chamber tubes, a temperature control of the actual thin-film vessel for photosynthesis can be achieved. Significant disadvantages of the use of double-chamber tubes consist in the technical connection of the chambers to the supply and discharge of the tempering medium and the culture medium without unwanted mixing of the two media takes place. This will be in the application DE 10 2009 045 851 A1 no suggestions made. The disadvantage of the technically complex connection of the inner and outer tube is also not solved.
The claimed in this application also of an inner tube which is guided by webs in the outer tube, also has significant disadvantages, because by this measure a flow resistance occurs and the deposition of microalgae and the associated "fouling" is favored. Fouling causes considerable costs. These costs are initially caused by deteriorated light and heat transfer. Furthermore, the environmental costs due to the necessary use of biocides to prevent biofouling or the increased use of energy to compensate for the reduced performance caused by fouling are to be seen.

Also known is a process in which initially an inoculate is cultivated in a closed photobioreactor and then in a fermenter without exposure to glucose growth is achieved up to a high microalgae concentration ( WO 2009/149794 A1 )

Similar describes DE 10 2008 059 562 A1 a process for the preparation of microalgae in which initially a stock culture is prepared by multiplication in photobioreactors under artificial exposure, then heterotrophically propagated in a fermentor without exposure to glucose and finally in a large photobioreactor using sunlight mixotroph to a ripe microalgae concentration is cultured ready.

As photobioreactors, not only tubular thin-film reactors are proposed, but also plate reactors ( DE 200 17 229 U1 ), eg made of acrylic glass ( WO 2015/032389 A1 ). By incorporating baffles into the circulation of the culture solution, the backmixing should be reduced. To increase productivity, artificial lighting with LED artificial light of specific wavelengths is proposed in addition to daylight. A temperature of the reactors is not described. Plate reactors have the fundamental disadvantage that the light required for photosynthesis can only penetrate from two sides, which does not optimally exploit the synthesis power.

Disadvantages of using methods with fermenters are the high investment costs, the cost of the food glucose and the fatigue of the stock cultures with increasing number of cultivation cycles. After a few cycles, a fresh stock culture grown in external photobioreactors must always be used for inoculation, otherwise the active substances typical of microalgae, such as e.g. Chlorophyll, can no longer be formed in sufficient quantities.

The disadvantages of most known methods are also that they are apparently only suitable for the production of small quantities in small plants (laboratory or pilot plants). Measures which seem to be suitable for the production of microalgae on an industrial scale, ie for industrial production, are not described or insufficiently described in the prior art. In particular, the required Investment costs and the required energy expenditure not described in such a way that also high quantities of microalgae can be achieved with high quality considering the economic efficiency.

Further disadvantages of some described processes for the production of microalgae are the proposed materials for the photobioreactors. In particular, this is on in the document DE 10 2009 045 851 A1 directed hose photobioreactor described. Synthetic polymers such as polymethacrylate, polyethylene, silicone rubber, polystyrene, and others, have the general disadvantage of photobioreactors for producing microalgae for nutrition compared to glass, that they must not contain traces of monomers from which they are made. These could be gradually released by leaching into the product microalgae. In addition, some of these polymeric materials are made using plasticizers. These too can be released slowly to the product. A complete removal of monomers or plasticizers is possible, but expensive and expensive the material for the photobioreactors considerably.

Polymers are also sensitive to the amount of ultraviolet radiation in sunlight and age more easily than, for example, glass. Glass is also cheaper than many of the proposed polymers for photobioreactors. Glass has been proven in practice for decades as a technical solution for photobioreactors for the production of microalgae ( www.algomed.de ), leaching and aging have not been observed. A disadvantage of glass photobioreactors, however, is that the glass tubes can not be arbitrarily brought into low-cost geometric shapes for photobioreactors.

Another disadvantage of photobioreactors made of glass tubes for the production of microalgae is that so far no technically sound and cost-effective direct temperature control is known. Jackets through an outer glass tube according to the principle of the Liebig cooler ( DE 10 2007 012 745 A1 ) are known, but expensive and too expensive for industrial plants.

Because of the need for sunlight for photosynthesis in industrial photobioreactors, a common technical solution is the arrangement of Photobioreactors in greenhouses and their tempering. This is a cost and energy intensive solution that is also not reasonable for every location.

The object of the invention is therefore to overcome the above-described disadvantages of the known methods and systems and to present a method and a system which are suitable for industrial biological, in particular for photochemical application.

According to the invention, the disadvantages of the known solutions are overcome by the features of claims 1 and 12.

Accordingly, the invention consists in a process for the preparation of microalgae in a tubular thin-film photobioreactor, which consists of glass tubes arranged in parallel, wherein the microalgae are recycled from a mixing and starting container and thereby cultivated in a culture solution, wherein the cultivation of the microalgae in the tubular thin-film photobioreactor with active temperature control and circulation by an internal cooling of the culture solution in phototrophic or mixotropher driving. For active temperature control in the glass tubes to a flexible hose is laid, which floats in the culture solution and through which a temperature control medium is pumped. Advantageously, the culture temperature is maintained above the minimum growth temperature and below the maximum growth temperature of the respectively cultured microalgae type by the tempering medium.
According to a particular feature of the invention, the temperature control medium in the flexible hose is periodically replaced by air. The air pulses lead to the periodic increase of the flexible tube and thereby advantageously prevent fouling, because the deposition of a biofilm is prevented.

The disadvantage of the obviously not yet solved high technical complexity of the implementation of an inner tube or one of the two chambers of a double-chamber tube in the already known tubular Dünnschichtphotobioreaktoren in and out of the reactor is achieved in that the flexible inner tube individually or as frets at the top or bottom chamber-shaped inflow and outflow of the parallel tubes is guided through the culture solution to the outside by means of classical installation technology, so that a mixing of temperature control medium or air with the culture solution is impossible.
It is envisaged that in the mixing and outlet container in the circulation of the culture solution for active temperature control a spiral tempering is arranged for cooling or heating, being used as a spiral tempering a consisting of an inert metal tube tempering, which is traversed by a tempering. The flexible tube and the spiral tempering can be traversed by the same temperature control. The total volume of the temperature control medium flowing through the flexible hose and the spiral-shaped temperature control element is between 1% and 20%, preferably 5% of the culture solution volume. However, a different temperature control medium can also be passed through the flexible hose in the circulation of the culture solution than through the spiral temperature control element.

According to a special feature, it is provided that the flexible tube and / or the spiral tempering element are provided on their outer surfaces wholly or partially with a protection against the deposition of a biofilm.

The disadvantages of the previously known methods, that is cultured by seasonal or daily time-related temperature peaks that are lower or higher than the optimal growth temperatures of microalgae, are arranged by the active temperature control according to the invention (internal cooling) by means of the tubular thin-film photobioreactor, of a Temperiermedium flowed through, flexible hose, which floats in the culture solution, overcome.

This can both a dying of the microalgae are avoided by excessive temperatures as well as in moderate latitudes earlier in the year and also longer in a year eien cultivating microalgae can be achieved. Both advantages of active temperature control increase both product quality and productivity compared to known methods.

The inventive solution of the active temperature control microalgae can be cultivated on an industrial scale cost in the future, even under climatic conditions under which it has not been economically possible.

The disadvantages of plate reactors are overcome by the already known use of tubular thin-film photobioreactors made of glass tubes. The use of glass tubes also overcomes the inherent disadvantage of using tubes or tubes made of organic polymers. The disadvantage of the high price of the hitherto proposed use of high-grade, but often more expensive, double-tube reactors made of silicone rubber is overcome by the use of glass tubes with an internally arranged, flexible hose through which a temperature control medium flows.

The potential deposition of micro-alveolar biomass in tubular tubular thin-film photobioreactors in continuous operation according to the invention is counteracted both by the choice of high-grade polymer material as the flexible tube material and by a special protection on the external surfaces and by the short-term replacement of the tempering medium by air, because by the choice of material a deposit is reduced and the tube is periodically moved within the glass tubes by buoyancy and pulsation. The "fouling" is thereby prevented or at least reduced.
The features of the system according to the invention are already apparent from the method features described above and the claims related to the system and the embodiments.

The invention will be described in more detail in the following embodiments.

example 1

In a tubular thin-film photobioreactor, microalgae of the species Chlorella vulgaris are cultured by the method according to the invention.

The tubular Dünschichtphotobioreaktor consists in the photoactive part tubes of leaching resistant borosilicate glass with an outer diameter of 60 mm and an inner diameter of 54 mm. The glass tubes are U-shaped, each leg is 50 m long. 22 of these U-shaped glass tubes are arranged one above the other at a distance of 20 cm in a frame. The inflow of the microalgae cultivating solution into and out of the 22 glass tubes takes place in each case through a comb-shaped collecting line. In all glass tubes is a flexible hose made food-safe polyethylene with an outer diameter of 20 mm and an inner diameter of 16 mm for the recording of a tempering arranged movably. The flexible tube in the glass tubes is individually fed into the comb-shaped manifolds and led out at the top or bottom of the manifolds of the culture solution using classical installation technology through the cap so that finally each 22 tubes outside the culture solution leave the frame with the 22 glass tubes and be merged into a single supply system for the temperature control medium.

The tempering medium is preferably water, which is brought to the required flow temperature in a conventional, external cooling or heating device. In the flow a valve system is arranged, which allows to feed controlled air pulses in the temperature control medium.

A unit of the tubular thin-film photobioreactor, consisting of 12 racks, each with 22 of the U-shaped glass tube systems as described above, with the chambered inflow and outflow systems, the manifolds, the supply system for the temperature control medium and a collection container in the circulation of the culture solution is placed in a greenhouse ,

The culture solution is circulated through the thin-film photobioreactor. The collecting container is a spiral tempering unit made of stainless steel tube with 60 mm outer diameter and with a wall thickness of 2 mm, consisting of 30 turns each with a diameter of 2 m. The spiral-shaped temperature control unit can optionally be flowed through by the same temperature control medium as the flexible hose in the glass tubes.

In the spring, on a site 52 ° north latitude with an average sunshine duration of 5.2 h / d, the cultivation of chlorella microalgae was performed by the method according to the invention. At the beginning of the cultivation of a stock culture with 0.3 g / l (dry biomass), the outside temperature was 12 ° C and the temperature in the greenhouse 15 ° C. The entire system for active temperature control was switched on, the flow temperature of the temperature control medium was 32 ° C. After 3 hours, the culture solution had reached a temperature of 26 ° C. This temperature was maintained by automatic control of the tempering medium. Every 45 minutes was for each 5 minutes air instead of the temperature medium passed through the flexible hoses. After 3 days, the microalgal density was 3.0 g / L. The growth rate was 0.9 g / ld. Such high growth rates are not yet described for such microalgae cultures at these seasons. Harvesting ended this cultivation.

Example 2

The same thin film photobioreactor system described in Example 1, but without the active temperature control system, was operated at the same site in the spring for the cultivation of chlorella microalgae. At the beginning of the culture of a stock culture with 0.4 g / l (dry biomass), the temperature in the greenhouse was 16 ° C. During the cultivation period of 3 days, the temperature in the greenhouse rose to a maximum of 22 ° C. At the end of the 3-day cultivation, the biomass concentration was 1.4 g / l. The growth rate was 0.33 g / Id.

Example 3

The same thin film photobioreactor system described in Example 1 was operated at the same site in the midsummer with the same stock culture of Chlorella microalgae and a starting concentration of 0.2 g / l in accordance with the invention.

The starting temperature of the culture solution was 27 ° C, the outside temperature at noon 36 ° C, in the greenhouse 42 ° C. After switching on the entire system for active temperature control with a flow temperature of 12 ° C, the temperature of the culture solution was limited to 32 ° C and held for 3 days. Every 45 minutes, air was passed through the flexible tubing for 5 minutes instead of the temperature control medium. After 3 days, the microalgal density was 3.2 g / l. The growth rate was 1 g / id. Microscopic examination of the culture solution revealed 99.6% intact chlorella cells. Harvesting ended this cultivation.

Example 4

The same thin film photobioreactor system described in Example 1, but without the system for active temperature control, became at the same location in midsummer operated with the same chlorella stock and a starting concentration of 0.2 g / l.

The starting temperature of the culture solution was 26 ° C. During the three-day cultivation, the temperature of the culture solution reached up to 43 ° C. The color of the culture solution had changed from green to brown-yellow. Microscopic examination of the culture solution revealed less than 4% intact chlorella cells. The biomass was discarded.

Claims (18)

Method of producing microalgae in a tubular thin-film photobioreactor consisting of glass tubes arranged in parallel, wherein the microalgae are recirculated from a mixing and starting container and cultured in a culture solution, characterized in that the cultivation of the microalgae in the tubular Thin-layer photobioreactor with active temperature control and circulation of the culture solution in phototrophic or mixotropher manner of driving takes place. A method according to claim 1, characterized in that for the active temperature control in the glass tubes, a flexible and floating in the culture solution hose is laid, through which a temperature control medium is pumped. Process according to claims 1 and 2, characterized in that the temperature control medium in the flexible hose is periodically replaced by air. A process according to claims 1 to 3, characterized in that the culture temperature is maintained above the minimum growth temperature and below the maximum growth temperature of the respectively cultured microalgae type by the tempering medium. Method according to one of claims 1 to 4, characterized in that in the mixing and output container in the circulation of the culture solution for active temperature control, a spiral tempering is arranged for cooling or heating. A method according to claim 5, characterized in that is used as a spiral tempering a consisting of an inert metal tube tempering, which is traversed by a tempering. Method according to one of claims 1 and 6, characterized in that the flexible tube and the spiral tempering are traversed by the same temperature control medium. A method according to claim 7, characterized in that the total volume of the flowing through the flexible tube and the spiral tempering temperature control medium is between 1% and 20%, preferably 5% of the culture solution volume. A method according to claim 1 to 8, characterized in that through the flexible hose, a different temperature control flows as through the spiral tempering in the circulation of the cultivation solution. A method according to claim 1 to 8, characterized in that the flexible tube and / or the spiral tempering are provided on their outer surfaces wholly or partially with a protection against the deposition of a biofilm. Process according to claims 1 to 10, characterized in that the process is carried out with the tubular thin-film reactor in a greenhouse. Plant for the production of microalgae in a tubular thin-film photobioreactor, wherein the plant comprises parallel glass tubes and at least one mixing and output container, characterized in that the system comprises means for active temperature control and circulation of the culture solution in phototrophic or mixotropher mode. Installation according to claim 12, characterized in that the tubular thin-film photobioreactor consists of borosilicate glass tubes with an internal diameter of 30 to 70 mm. Installation according to claims 12 and 13, characterized in that the active temperature control in the borosilicate glass tubes an exposed flexible hose is arranged, which floats freely in the culture solution and through which a temperature control medium can be conveyed. Installation according to one of claims 12 to 14, characterized in that in the mixing and outlet container in the circulation of the culture solution for active temperature control, a spiral tempering is arranged for cooling or heating. Plant according to claim 15, characterized in that a tempering element consisting of an inert metal tube, which can be flowed through by a tempering medium, is arranged as a spiral tempering element. Installation according to claims 11 to 16, characterized in that the outer surfaces of the flexible tube and / or the spiral tempering completely or partially have a protection against the deposition of a biofilm. Installation according to claims 11 to 17, characterized in that it is arranged in a greenhouse.